[dabreegster]

Especially if you're trying to clip your entire map to some boundary, rendering the ocean is hard. https://github.com/a-b-street/abstreet/issues/32 has some examples of "flooded" maps when the heuristics get the inversion wrong. https://github.com/a-b-street/abstreet/blob/9761373c4b215485... is my incomplete attempt to deal with these partial multipolygons.

[kqr]

Potentially dumb suggestion: what if one just declares anything that has a significant chunk of non-bridge or non-tunnel street on it land? It's not a universal solution but perhaps sufficient for the application?

[mvh]

I recently made a map (using Generic Mapping Tools) of one of the Aleutian Islands in Alaska, for one of my dad’s grad students to use in a paper. That would constitute a good example of where you couldn’t just tell my # of built structures (since at certain zoom levels, there are none!)

[kqr]

Sure, but are you likely to have users want to A/B test traffic light configurations there? My suggestion was very specific to the application in question.